Coupling arrangement



Oct. 3, 1933. p. G. EDWARDS 1,928,720

COUPLING ARRANGEMENT Filed Feb. 27, 1930 mvENToR BYZ? Edwarmis V ATTORNEY Patemed oct. 3, 1933l coUPLING ARRANGEMENT Paul G. Edwards, Bloomfield, N. J., assigner to American Telephone and Telegraph Company, a corporation of New York Application February 27, 1930. Serial No. 431,808

' 3 Claims.

This invention relates generally to signaling systems. More particularly, it Arelates to systems for the transmission of currents within bands of different frequency components which are of sub- A stantially equal widths.v Still more particularly, this invention relates to arrangements for selectively receiving the c urrents within anyone of a plurality of bands all occupying different'positions in the frequency spectrum' and havingthe same widths. In a radio broadcast system, it is necessary to employ apparatus capable of selectively receiving any one of a plurality of programs all of which are represented by bands of frequencies of substantially equal widths. The selection of any one of the various programs may be obtained by `vary-- ing one or more of the reactive elements of the receiving apparatus ina manner well understood in the art. It has been found that one setting of the reactive elements permits thevreceptionof a band of frequencies ofy one width, and a different setting of these reactive elements permits the reception of another band of frequencies of a substantially different width. When the received band is'toov narrow, some of its component currents become suppressed and, therefore, the quality of the program is greatlydistorted. On the other hand, if the width of the band received is too great, too many currents'of adjacent programsbecome introduced into thereceiving apparatus, and these similarly interfere with the efficient reproduction of the desired program matter. The need for apparatus capable of eili-A ciently transmitting any one of a plurality of programs represented by bands of different frequencies occupying equal spaces in the spectrum, Vis very important and it is as important in carrier and other signaling systems as it is in radio broadcasting. 1

One ofthe objects of this invention is to provide an arrangement for selectively transmitting any one of a plurality of different bands of frequencies which have substantially the same widths.

Another of the objects'of this invention is to providean arrangement for shifting the limits of currents to be freely transmitted from one position in the frequency spectrum to another position in the spectrum so that these limits may 50 remain of the same width.

. Other and further objects of this invention will be apparent from the detailed description of the invention hereinafter following when read in connection with the accompanying drawing in which i 55 Figure 1 discloses an arrangement including the lthe radio art.

elements generally required in practicing the inv venton; Fig. 2 shows a circuit electrically equivalent to the one shown in Fig. 1; Fig. 3 shows curves illustrating the various features of the invention; and Fig. 4 shows a vacuum tube systemfor selec- 60 tively transmitting the Vcurrents within any one of I a plurality of different bands of frequencies which have substantially equal widths.

Fig. 1 of the drawing discloses the elements generally required in `carrying out the principles ofr thisv invention. HIt includes a transformer T which has two windings L1 and L2 inductively related topeach other. These windings are designed to exhibit the same inductances', and their mutual reactance may be made as large or as small as 'AIO desirable, as is well understood in the art. Condensers C1 and C2 are both of the variable type and they are preferably equal in their exhibited capacities.. These condensers may be simultaneously operated and lvaried to the same extent 'I5 by mechanical coupling meanswhich may take the form of a commonshaft, as is well known in Another condenser C0 of a predetermined capacity may be connected between the lower terminals of the windings L1 and Lz of ,230 the transformer T and the lower terminals of the 1 condensers C1 and C2, as shown.v

The arrangement shown in Fig. 1 of the drawing involves two local circuits which are electrically coupled. One of these circuits includes the y8.5 condenser C1, the winding L1 and the condenser Co, andthe other includes the condenser C2, the

winding VLaand the condenser Co. The mutual reactance between windings L1 and L2 is elTectively in series with the reactance of the condenser C0. In accordance with this invention,

the mutual reactance of these windings is made of a negative o rder so that this reactance may be additive in effect with that of-the condenser If these windings are found to .exhibit a positive mutual reactance, thisreactance may be made of anegative order merely by the reversal of one of the windingswith respect to the other. Fig. 2 of the` drawing schematically represents a circuit electrically equivalent to the one shown in Fig. Y1 after the condenser C1 and C2 are both set at a common and definite, predetermined capacitive Value. The inductances L-L simulate the inductances of the windings L1 and L2 of the transformer T. The capacities C-C are equal to theVV capacities of condensers C1 and C2. The

condenser C0 represents the capacity of the condenser Co of Fig. 1, while the inductance M rep.-

resents the mutual inductance of the windings reactance so as to have an effect which is additive with respect to the reactance of condenser Co.

When a voltage is impressed in series with either of the capacities C--C, then the total reactance of the circuit will be represented by the o following expression:

Setting this expression equal to zero in'order to determine the frequencies Yof resonance and simplifying the resultant equation, then the following expression may be obtained:

The value of 12 may be found from thefollowing equation: l

w2`='2LC2+2`LCCo,-2CMCoi(2LC2+2CMC0) (3) Two values of 12 will be obtained from Equation (3), and 'these will be determined by the follow- One of the resonant frequencies 4will be determined by the square root of the expression at the right'hand side of the sign of equality in 1. be approximately their mid-capacities.

Equation (4*) lAnother of the resonant frequencies will be similarly determined by the square root of the expression at the right hand side of the sign of equality in'Equation (5).

In `order that the band of frequencies transmitted by the arrangement involved in this invention may be highly constant in width over a rangewhich may, for example, be associated with a carrier frequency or, for example, some frequency midway between the limits of some desired band, itwill be necessary to make the ratio of the mutual inductance M tothe inductance L the same as the ratio of the capacity of condenser Cu tothe particular -value ofthe capacity C. It

will be understood that the capacity C represents set at some effective value, which for the deterl mination of the above-mentioned equality, should It will be understood that` the mid-capacity referred to herein represents half ythe sum of ther maximum and minimum capacities obtainable upon adjustment of the rotatable elements of either of the condensers C1 or C2. Thus, it will be apparentthat the inductive coupling coefficient must be made equal to the' average capacitive coupling coelcient in the practice of this invention.

The curves a, b and c of Fig. 3 are plotted with the capacity of either of the condensers C1 or C2 of Fig. 1 as abscissae, and the band widths obtained by variations in thecapacities of condensers C1 and lCz as ordinates. The curve a will be obtained from an inductive coupling between the two local circuits, in which case the condenser Cn will be omitted from consideration. The Vcurve b will be obtained when the two localcirc'uits are capaciitively coupled, in which case there kwill be no mutual inductance between these circuits. The rst of these curves shows that the band of frequencies transmitted decreases in width with an increase in capacity, and the second ofv these curves indicates that the band width increases with each increase in capacity. The curve c represents the sums of the ordinates of the curves a and b. Curve c clearly indicates that throughout the broad range of variation in the capacities of condensers C1 land Cz, the width of the band transmitted will be substantially constant.

If Vit is desired to increase the width of the transmitted band, it will be necessary to increase the amount of inductive coupling as well as the amount of capacitive coupling While maintaining the ratio of the mutual inductance M to the inductanceLthe same as the ratio of the capacity of condenser C0 to the mid-capacity of either of the condensers C1 or C2. Similarly, the width of the band transmitted may be decreased by decreasing the amounts of the inductive and capacitive couplings while maintaining the coupling coefficients in the same ratio. Thus, the width of the band may be increased by increasing the negative reactance of the mutual inductance and by decreasing the capacity of the condenser Co. Similarly, the width of the band may be decreased by decreasing the negative reactance of the mutual inductance and by increasing the capacity of the vcondenser Co. It will be found that the change in the -width of the band transmitted by the arrangement described herein will be directly proportional to the changes in the inductive and capacitive couplings. i

Fig. 4 shows a vacuum tube system forselectively transmitting ,any one' of al plurality of bands of frequencies, which .may have the same connected to its filament electrode'through the winding La of the transformer T and a battery B2. The filament electrodes of the tubes may be connected to batteries B3 and B4. Itrwll be apparent that the lower terminal of the winding L1 is grounded through batteries B1 and B3, and that the lower terminal ofthe winding L2 is grounded through the battery Bz.

The upper terminals of the windings L1 and Lz of the transformer T yare .connected in series with equal condensers C1 and C2 which may be varied in their capacitieslto the same extent. The midpoint of these condensers, i. e. the conductor common to their adjacent electrodes, is connected to ground through a condenser Co. The

vacuum tube V1 should preferably be one in vwhich i the drawing may be inductively coupled to an transmitted by the vacuum tube system. In I either case adjustments of the condensers C1 and C2 will permit the free transmission of any one of the bands impressed upon the input circuit O1, and the width of the band transmitted will remain the same regardless of the band selected.

It will be understood that the coupling arrangement characteristic of this invention may be connected between an antenna circuit and a vacuum tube system in such a manner that a portion of the high frequency energy 'impressed upon the antenna circuit will be introduced into the coupling arrangement. The coupling arrangement will then transmit a band of high frequencies, the position in the spectrum of which may be adjusted in the manner already discussed hereinabove.

While this invention has been shown and described in certain particular arrangements for the purpose of illustration, it will be understood that the general principles of thisinvention may be applied to other and vwidely varied organizations without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

l. A coupling arrangement for freely transmitting any one of a plurality of bands lof frequencies which occupy different positions in the frequency spectrum and which have the same widths. including two equal circuits each comprising a winding and a condenser, a circuit common to said equal circuits comprising a condenser, the mutual inductive reactance of said windings Ybeing negative and additive to the reactance of the condenser of the common circuit, and means for simultaneously varying the capacity of the condensers of said two equal circuits by equal amounts.

2. A coupling arrangement for freely transmitting any one of a plurality of bands of frequencies having the same definite and controllable width,

including two equal circuits each comprising a winding and a variable condenser, the` windings of said two equal circuits being mutually inductive, a circuit common to said equal circuits comprising a condenserwhich is effectively in series with the mutual inductance of said windings, the Y ratio of the capacity of the variable condenser of each ofsaid equalcircuits to the capacity of the condenser of the common circuit being equal-to the ratio of the mutual inductive reactance of the windings of said equal circuitsto the inductive reactance of each winding of said equal circuitsat the mid-capacity of each ofthe variable condensers.

3. In a system for freely transmitting any one of a plurality of bands of frequencies each` of which whenrtransmitted has a width in cycles'A which is constant and controllable, the combinatween the conductor common to said equal and variable condensers and ground, the ratio of the mutual inductanee between the windings of the transformer to the inductance of either of said windings being substantially the same as the ratio of the capacity of the xed condenser to the capacity of either of said variable condensers.

PAUL G. EDWARDS. 

